#include<bits/stdc++.h>
using namespace std;
double x_1,y_1,x_2,y_2;
int main(){
	while(scanf("%lf %lf %lf %lf",&x_1,&y_1,&x_2,&y_2)!=EOF){
		printf("%.2f\n",sqrt((x_1-x_2)*(x_1-x_2)+(y_1-y_2)*(y_1-y_2)));
	}
	return 0;
}
